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[IRCE] Don't iterate on loops that were cloned out

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IRCE has the ability to further version pre-loops and post-loops that it
created, but this isn't useful at all.  This change teaches IRCE to
leave behind some metadata in the loops it creates (by cloning the main
loop) so that these new loops are not re-processed by IRCE.

Today this bug is hidden by another bug -- IRCE does not update LoopInfo
properly so the loop pass manager does not re-invoke IRCE on the loops
it split out.  However, once the latter is fixed the bug addressed in
this change causes IRCE to infinite-loop in some cases (e.g. it splits
out a pre-loop, a pre-pre-loop from that, a pre-pre-pre-loop from that
and so on).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278617 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das 2016-08-14 01:04:36 +00:00
parent abf7d54189
commit 300cd13205
2 changed files with 37 additions and 0 deletions
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12
lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -79,6 +79,8 @@ static cl::opt<int> MaxExitProbReciprocal("irce-max-exit-prob-reciprocal",
static cl::opt<bool> SkipProfitabilityChecks("irce-skip-profitability-checks",
cl::Hidden, cl::init(false));
static const char *ClonedLoopTag = "irce.loop.clone";
#define DEBUG_TYPE "irce"
namespace {
@ -630,6 +632,11 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE, BranchProbabilityInfo &BP
BasicBlock *Latch = L.getLoopLatch();
assert(Latch && "Simplified loops only have one latch!");
if (Latch->getTerminator()->getMetadata(ClonedLoopTag)) {
FailureReason = "loop has already been cloned";
return None;
}
if (!L.isLoopExiting(Latch)) {
FailureReason = "no loop latch";
return None;
@ -913,6 +920,11 @@ void LoopConstrainer::cloneLoop(LoopConstrainer::ClonedLoop &Result,
return static_cast<Value *>(It->second);
};
auto *ClonedLatch =
cast<BasicBlock>(GetClonedValue(OriginalLoop.getLoopLatch()));
ClonedLatch->getTerminator()->setMetadata(ClonedLoopTag,
MDNode::get(Ctx, {}));
Result.Structure = MainLoopStructure.map(GetClonedValue);
Result.Structure.Tag = Tag;

25
test/Transforms/IRCE/unhandled.ll
View File

@ -70,5 +70,30 @@ define void @multiple_latches(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
ret void
}
define void @already_cloned(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
entry:
%len = load i32, i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%abc = icmp slt i32 %idx, %len
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32, i32* %arr, i32 %idx
store i32 0, i32* %addr
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit, !irce.loop.clone !{}
out.of.bounds:
ret void
exit:
ret void
}
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}